Quite often structures, such as building, patios and the like, are constructed on earth having a composition and density that is unable to bear the weight of the structure without settling. The foundations for these structures inevitably settle unevenly which causes the structure to lean and/or the foundation to crack. This type of settlement, if left unattended, creates an endless realm of problems.
In the past, conventional systems have been proposed for lifting the structure to, and supporting the structure at or near, its original unsettled position for the remainder of its useful life. For instance, U.S. Pat. Nos. 4,854,782 and 4,634,319 disclose apparatuses which drive individual piers or pilings vertically downward along side the structure until the piers or piles reach bedrock or a load bearing strata region, at which the piers experience a desired amount of resistance. Once the piers are driven to a desired depth, the foundation of the structure is raised by a desired amount and fastened to the piers with a bracket assembly. The piers and bracket assemblies are coupled to one another in order to support the building for an indefinite period of time. Hereafter, the piers, pilings, screw-type underpinnings, and the like are collectively referred to by any of these terms and simply as "underpinnings."
An alternative apparatus has been proposed (U.S. Pat. No. 4,800,700) for lifting and supporting concrete slabs, concrete floors and the like, that have settled and need to be righted or leveled to cure and prevent cracks and other structural defects. The apparatus of the '700 patent supports the slab by (1) cutting a plurality of access holes in the slab, (2) inserting a lift plate through each access hole, (3) rotating and drawing each lift plate against the underside of the slab, and (4) driving underpinning piers through the access holes to bedrock or a desired load bearing strata. After the necessary number of piers are driven, hydraulic rams are attached to the lifting plates and used to raise the slab to a desired level. Subsequently, the lifting plates are permanently secured to the piers and function as an underpinning support for the slab. The U.S. Pat. Nos. 4,800,700; 4,854,782; and 4,634,319 are incorporated herein by reference.
However, when using a hydraulic ram to drive pilings into the ground, the ram exerts a substantial upward force. Thus, it is necessary to exert an equal and opposite downward force upon the hydraulic rams to drive the pilings into the ground. Heretofore, this equal and opposite force was obtained by fastening the hydraulic rams to the side of the foundation, or the underside of the slab, and relying upon the structure's dead weight and any weights that could be hung on the drive assembly.
Often it is desirable to drive the piers to bedrock or a load bearing strata which exerts a force upon the piers that exceeds the weight of the structure. Also, in order to reach bedrock or a desired load bearing strata, it is often necessary to drive piers through an intermediate layer of material which is extremely dense or compacted. For instance, fill material may be dumped on an inclined surface and compacted to provide a level surface for supporting a foundation, only to settle after the building is erected. Also, the intermediate layer may simply represent a clay region or the like. In either situation, the compacted fill or clay region will be denser than the underlying soils. Accordingly, the underpinning drive assembly will experience greater resistance when the pier is forced through the fill material or clay, as compared to a lesser resistance experienced when driving the pier through the uncompressed underlying soils. Heretofore, when such dense regions were encountered, the hydraulic ram simply raised the foundation without driving the pier through the fill or clay region.
To compensate for this problem when underpinning a concrete slab, such as a patio, the systems of the '319 and '700 patents provide L-shaped wings on opposite sides of the bracket assembly to hold metal plates which added weight to the dead weight of the structure. However, during operation, it was necessary to separately add and remove these weights. Also, the systems of the '319 and '700 patents are intended for use with concrete slabs which do not support a structure. Thus, the concrete slab did not offer a large amount of dead weight, as compared to a building. Also, slight increases, through the addition of stationary weights, were sufficient to reach a load bearing strata sufficient to support a concrete slabs.
A variety of alternative methods have been proposed for supporting existing structures, such as in U.S. Pat. Nos. 5,213,448; 5,171,107; 5,139,368; 5,120,163 and 5,011,336. Each of these underpinning methods utilized screw-type underpinnings, in place of piers, which were driven to a desired depth. An underpinning bracket assembly was coupled between the screw-type underpinning and the foundation and the screw-type underpinning was used to support the foundation in place of the piers. However, these alternative methods relied on the dead weight of the drilling unit to force the screw-type underpinning downward. Thus, the screw-type underpinning was also unable to penetrate overly hard layers.
The need remains in the industry for improved designs and implementation techniques to address the problems and drawbacks heretofore experienced. The primary objective of this invention is to meet this need.